This invention relates to a magnetic material for magnetic recording media, which material is of the type comprising acicular particles of a magnetic substance.
Magnetic recording media such as tapes for magnetic recording are produced commonly by coating a plastic base with a magnetic material which is a dispersion of a magnetic powder in a liquid phase binder and thereafter solidifying the binder on the base by drying. To produce a magnetic tape which exhibits a relatively high rectangular ratio, usually use is made of a magnetic material whose magnetic component is a magnetic powder having a needle-like or acicular particle shape, and the base coated with the magnetic material is passed through a magnetic field before drying of the coating in order to orient the acicular particles such that the major axis of each particle becomes parallel to the direction of the magnetic field. A high rectangular ratio tape obtained through the orientation process exhibits excellent recording and reproducing characteristics.
Theoretically, the rectangular ratio of the tape can be raised by increasing the magnetic field strength for the orientation. In practice, however, it is almost impossible to make the strength of a magnetic field for the orientation more than about 3000 oersteds by means of a permanent magnet. In the case of using a coil, a huge apparatus and a corresponding power source are required to produce a magnetic field of a desirably high strength. Accordingly there is a limit to the magnetic field strength of the orientation process. Besides, the application of an excessively high strength magnetic field to the tape for the purpose of orientation tends to impair the surface smoothness of the magnetic coating.